Semiconductor device
An embodiment is a semiconductor device which includes a first oxide semiconductor layer over a substrate having an insulating surface and including a crystalline region formed by growth from a surface of the first oxide semiconductor layer toward an inside; a second oxide semiconductor layer over the first oxide semiconductor layer; a source electrode layer and a drain electrode layer which are in contact with the second oxide semiconductor layer; a gate insulating layer covering the second oxide semiconductor layer, the source electrode layer, and the drain electrode layer; and a gate electrode layer over the gate insulating layer and in a region overlapping with the second oxide semiconductor layer. The second oxide semiconductor layer is a layer including a crystal formed by growth from the crystalline region.
1. A semiconductor device comprising:
a gate electrode over a substrate;
a gate insulating layer over the gate electrode;
an oxide semiconductor layer over the gate insulating layer; and
source and drain electrodes electrically connected to the oxide semiconductor layer,
wherein:
the oxide semiconductor layer comprises a first region and a second region;
the first region is closer to the substrate than the second region;
the second region comprises a crystalline region; and
the crystalline region includes crystals whose c-axes are aligned.
2. The semiconductor device according to claim 1 , wherein the second region has a higher electric conductivity than the first region.
3. The semiconductor device according to claim 1 , wherein the crystalline region has a c-axis orientation.
4. The semiconductor device according to claim 1 , wherein the crystalline region includes crystals aligned in a direction perpendicular or substantially perpendicular to a surface of the oxide semiconductor layer.
5. The semiconductor device according to claim 1 , wherein:
the first region includes a two-component metal oxide; and
the second region includes a three-component metal oxide.
6. The semiconductor device according to claim 5 , wherein:
the two-component metal oxide includes an In—Zn—O-based material; and
the three-component metal oxide includes an In—Ga—Zn—O-based material.
7. A semiconductor device comprising:
an oxide semiconductor layer over a substrate;
source and drain electrodes electrically connected to the oxide semiconductor layer;
a gate insulating layer over the oxide semiconductor layer and the source and drain electrodes; and
a gate electrode over the gate insulating layer,
wherein:
the oxide semiconductor layer comprises a first region and a second region;
the first region is closer to the substrate than the second region;
the second region comprises a crystalline region; and
the crystalline region includes crystals aligned in a direction perpendicular or substantially perpendicular to a surface of the oxide semiconductor layer.
8. The semiconductor device according to claim 7 , wherein the second region has a higher electric conductivity than the first region.
9. The semiconductor device according to claim 7 , wherein the crystalline region has a c-axis orientation.
10. The semiconductor device according to claim 7 , wherein the crystalline region includes crystals whose c-axes are aligned.
11. The semiconductor device according to claim 7 , wherein:
the first region includes a two-component metal oxide; and
the second region includes a three-component metal oxide.
12. The semiconductor device according to claim 11 , wherein:
the two-component metal oxide includes an In—Zn—O-based material; and
the three-component metal oxide includes an In—Ga—Zn—O-based material.
13. A semiconductor device comprising:
a first gate electrode over a substrate;
a first gate insulating layer over the first gate electrode;
an oxide semiconductor layer over the first gate insulating layer;
source and drain electrodes electrically connected to the oxide semiconductor layer;
a second gate insulating layer over the oxide semiconductor layer and the source and drain electrodes; and
a second gate electrode over the second gate insulating layer,
wherein:
the oxide semiconductor layer comprises a first region and a second region;
the first region is closer to the substrate than the second region;
the second region comprises a crystalline region;
the first region includes a two-component metal oxide; and
the second region includes a three-component metal oxide.
14. The semiconductor device according to claim 13 , wherein the second region has a higher electric conductivity than the first region.
15. The semiconductor device according to claim 13 , wherein the crystalline region has a c-axis orientation.
16. The semiconductor device according to claim 13 , wherein the crystalline region includes crystals whose c-axes are aligned.
17. The semiconductor device according to claim 13 , wherein the crystalline region includes crystals aligned in a direction perpendicular or substantially perpendicular to a surface of the oxide semiconductor layer.
18. The semiconductor device according to claim 13 , wherein:
the two-component metal oxide includes an In—Zn—O-based material; and
the three-component metal oxide includes an In—Ga—Zn—O-based material.